#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <queue>
#include <string>
#include <map>
#include <set>
#include <stack>
#include <tuple>
#include <deque>
#include <array>
#include <numeric>
#include <bitset>
#include <iomanip>
#include <cassert>
#include <chrono>
#include <random>
#include <limits>
#include <iterator>
#include <functional>
#include <sstream>
#include <fstream>
#include <complex>
#include <cstring>
#include <unordered_map>
#include <unordered_set>
using namespace std;

// #pragma GCC optimize("O3")
// #pragma GCC optimize("unroll-loops")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,tune=native")
// #pragma GCC target("avx512f,avx512dq,avx512cd,avx512bw,avx512vl")

using ll = long long;
constexpr int INF = 1001001001;
constexpr int mod = 1000000007;
// constexpr int mod = 998244353;

template<class T>
inline bool chmax(T& x, T y){
    if(x < y){
        x = y;
        return true;
    }
    return false;
}
template<class T>
inline bool chmin(T& x, T y){
    if(x > y){
        x = y;
        return true;
    }
    return false;
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int N, M;
    cin >> N >> M;
    vector A(N, vector<ll>(M));
    vector<ll> S(N);
    for(int i = 0; i < N; ++i){
        for(int j = 0; j < M; ++j){
            cin >> A[i][j];
            S[i] += A[i][j];
        }
    }

    constexpr ll inf = 1e+17;
    vector dp(N + 1, vector<ll>(2, -inf));
    dp[0][0] = 0;
    for(int i = 0; i < N; ++i){
        for(int j = 0; j < 2; ++j){
            if(dp[i][j] == -inf)    continue;
            chmax(dp[i + 1][j], dp[i][j]);
            chmax(dp[i + 1][j ^ 1], dp[i][j] + S[i] * (j ? -1 : 1));
        }
    }

    cout << max(dp[N][0], dp[N][1]) << endl;

    return 0;
}